Cyclohexenones epoxidation

Successful asymmetric epoxidation of 2-cyclohexen-l-one was achieved using /-butyl hydroperoxide, toluene, solid sodium hydroxide, and benzylquininium chloride. Cyclohexenone epoxide obtained in this manner has an e.e. of 20% ([ ] = -39°). 

Mn(TPP)I04 02 + toluene, cyclohexene or cyclopentane Benzaldehyde, cyclohexenone, epoxide, or cyclopentanone Solvent benzene Xlrr = 310-490 nm selective conversion of toluene to benzaldehyde, and cyclopentane to cyclopentanone using C104 the reactions are stoichiometric [159]... 

Table 3.3-6 Result of one-pot preparation of optically active epoxides 96a-d by a combination of cyclohexenone epoxidation and enantiomeric resolution in a water suspension medium.

Epoxides are reactive substrates, which can easily be isomerized to give aldehydes or ketones. Kulawiec and coworkers have combined a Pd-catalyzed isomerization of mono and diepoxide 6/1-348 or 6/1-349 and 6/1-352 or 6/1-353, followed by an aldol condensation to give either cyclopentenones or cyclohexenones 6/1-350, 6/1-351, 6/1-354 and 6/1-355, respectively (Scheme 6/1.89) [165]. 

Inductions Obtained by Varying the Base in the Epoxidation of Cyclohexenone and Chalcone with /-Butyl Hydroperoxide (77)... 

Asymmetric epoxidathn (7, 311 8, 430) Optically active epoxides of cyclohexenones can be obtained by epoxidation with /-butyl hydroperoxide in toluene with solid NaOH and (-)-benzylquininium chloride as the chiral catalyst. In the case of a cyclohexenone the chemical yield is 60% and the optical yield is 20 3%. ... 

Coupling our own methodology with research developed by Wender et al.25 allowed us to devise a five-step sequence for the preparation of the cyclialkylation precursor 63 (Scheme 5.6). In the first step, the organolithium species 60 derived from isopropyl-veratrole24 was used to prepare cyclohexenone 61 through reaction with epoxide 59.25 The... 

Similarly, 2-cyclohexenone (Eq. 77) gave the desired epoxide w 66% yield, and benzalacetophenone (Eq. 7S) gave the correspond g epoxide nearly quantitatively. 

Epoxide formation is nearly suppressed when massively subeti-tuted olefine, such as 2,2,4-trimethyl-3-hexene among others, ate subjected to the chromic oxide-acetic anhydride reagent,42 Cyclo-hexene yields primarily 2-cyclohexenone and cyclohexane- 1,2-dione777 although some cyclohexane oxide appears to bo formed also (Eq, 111). 

Spiro epoxidation of a -enones.1 The conversion of ketones to spiro epoxides is usually carried out with dimethylsulfonium methylide, but this reaction can proceed in low and variable yields when extended to a,p-enones. A generally useful route to these vinyl spiro epoxides involves addition of 1, methylation, and ring closure with base, as illustrated for cyclohexenone. 

Considering only the three mild oxidation products in the liquid phase, it can be inferred that the photocatalytic oxidation of cyclohexene occurs at two sites of the molecule mainly the allylic position (86 %), giving the cyclohexenone and the cyclohexenol, and, to much lesser extent, the double bond (14 %) yielding the epoxide. 

The oxidation of cyclohexene was systematically investigated by means of metal porphyrins which have distinct redox potentials due to different metals [134]. The best results were obtained with Mn(III)TPP/L-Cys/NaBH4 which furnished a product mixture consisting of cyclohexenone (46.4%) > cyc-lohexanol (23.8%) > cyclohexenol (19.5%) > cyclohexanone (9.0%) > epoxide (1.4%), relative yields given in parenthesis. In the presence of KOH and riboflavin as an electron transfer reagent the product distribution was similar but the total yield was considerably improved [135]. 

Gold-catalyzed oxidation of styrene was firstly reported by Choudhary and coworkers for Au NPs supported on metal oxides in the presence of an excess amount of radical initiator, t-butyl hydroperoxide (TBHP), to afford styrene oxide, while benzaldehyde and benzoic acid were formed in the presence of supports without Au NPs [199]. Subsequently, Hutchings and coworkers demonstrated the selective oxidation of cyclohexene over Au/C with a catalytic amount of TBHP to yield cyclohexene oxide with a selectivity of 50% and cyclohexenone (26%) as a by-product [2]. Product selectivity was significantly changed by solvents. Cyclohexene oxide was obtained as a major product with a selectivity of 50% in 1,2,3,5-tetramethylbenzene while cyclohexenone and cyclohexenol were formed with selectivities of 35 and 25%, respectively, in toluene. A promoting effect of Bi addition to Au was also reported for the epoxidation of cyclooctene under solvent-free conditions. 

Catalyst Substrate Cyclohexenol Cyclohexenone Cyclohexene Epoxide TNb c... 

Silylcyclopropanation. This ylide reacts with a,/3-unsaturated cyclohexenones and cyclopentenones to give silylcyclopropyl ketones in fair yields (35-65%). The method by which 1 is generated is extremely important for this reaction. Neither t-nor n-butyllithium can be used as base. Epoxides, which would have resulted from desilylation to dimethylsulfonium raethylide, are not formed. 

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